U.S. patent application number 15/773994 was filed with the patent office on 2018-11-08 for sound output apparatus.
The applicant listed for this patent is MODA-INNOCHIPS CO., LTD.. Invention is credited to In Seob JEONG, Young Sul KIM, Sang Hun PARK, Sung Chol PARK.
Application Number | 20180324519 15/773994 |
Document ID | / |
Family ID | 60931589 |
Filed Date | 2018-11-08 |
United States Patent
Application |
20180324519 |
Kind Code |
A1 |
PARK; Sung Chol ; et
al. |
November 8, 2018 |
SOUND OUTPUT APPARATUS
Abstract
The present disclosure provides a sound output apparatus
including a first sound output unit, a second sound output unit
spaced a predetermined distance from the first sound output unit,
at least one opening defined in the second sound output unit, and a
housing for accommodating at least one of the first and second
sound output units. Here, the housing has an external diameter that
is 100% to 130% of a diameter of the second sound output unit.
Inventors: |
PARK; Sung Chol; (Ansan-Si,
Gyeonggi-Do, KR) ; KIM; Young Sul; (Seoul, KR)
; PARK; Sang Hun; (Seoul, KR) ; JEONG; In
Seob; (Ansan-Si, Gyeonggi-Do, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MODA-INNOCHIPS CO., LTD. |
Ansan-Si, Gyeonggi-Do |
|
KR |
|
|
Family ID: |
60931589 |
Appl. No.: |
15/773994 |
Filed: |
June 7, 2017 |
PCT Filed: |
June 7, 2017 |
PCT NO: |
PCT/KR2017/005907 |
371 Date: |
May 4, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04R 1/1058 20130101;
H04R 9/02 20130101; H04R 23/02 20130101; H04R 2201/029 20130101;
H04R 1/28 20130101; H04R 17/00 20130101; H04R 1/24 20130101; H04R
9/06 20130101; H04R 17/005 20130101 |
International
Class: |
H04R 1/28 20060101
H04R001/28; H04R 17/00 20060101 H04R017/00; H04R 23/02 20060101
H04R023/02; H04R 9/02 20060101 H04R009/02; H04R 1/10 20060101
H04R001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 2016 |
KR |
10-2016-0072555 |
Apr 4, 2017 |
KR |
10-2017-0043659 |
Claims
1. A sound output apparatus comprising: a first sound output unit;
a second sound output unit spaced a predetermined distance from the
first sound output unit; and a housing configured to accommodate at
least one of the first and second sound output units, wherein at
least one of the first and second sound output units comprises a
piezoelectric element in which a plurality of piezoelectric layers
are laminated, and the piezoelectric element is formed in at least
one of manners that the piezoelectric layer has a thickness that is
1/3 to 1/100 of that of the piezoelectric element, and the
laminated number of the piezoelectric layers is 2 to 50.
2. The sound output apparatus of claim 1, wherein the other of the
first and second sound output units is a dynamic speaker and
disposed in the housing.
3. The sound output apparatus of claim 1, further comprising at
least one opening defined in the piezoelectric element.
4. The sound output apparatus of claim 3, wherein the at least one
opening has a diameter that is 3% to 70% of that of the
piezoelectric element.
5. The sound output apparatus of claim 1, wherein an external
diameter of the housing is 100% to 130% of a diameter of the
piezoelectric element.
6. The sound output apparatus of claim 5, further comprising a
vibration plate provided on one surface of the piezoelectric
element and having an external diameter that is equal to or less
than that of the housing.
7. The sound output apparatus of claim 6, wherein the vibration
plate is seated on an upper portion of the housing.
8. The sound output apparatus of claim 1, wherein the piezoelectric
element comprises a plurality of piezoelectric layers, a plurality
of internal electrodes provided between the plurality of
piezoelectric layers, and an external electrode provided at the
outside in order to be connected to the plurality of internal
electrodes.
9. The sound output apparatus of claim 8, wherein each of the
piezoelectric layers has a thickness of 2 .mu.m to 50 .mu.m.
10. (canceled)
11. (canceled)
12. The sound output apparatus of claim 8, wherein each of the
piezoelectric layers has a thickness equal to or greater than that
of an internal electrode.
13. The sound output apparatus of claim 8, wherein the
piezoelectric layer comprises at least one pore.
14. The sound output apparatus of claim 8, wherein an internal
electrode has at least one area having a different thickness.
15. The sound output apparatus of claim 8, wherein an internal
electrode has a surface area that is 10% to 97% of that of the
piezoelectric layer.
16. The sound output apparatus of claim 1, wherein the
piezoelectric layer comprises a seed composition.
17. The sound output apparatus of claim 1, wherein the
piezoelectric layer comprises an oriented base material composition
made of a piezoelectric material having a perovskite crystal
structure and a seed composition made of an oxide distributed in
the oriented base material composition and having a general formula
of ABO.sub.3 (A indicates a divalent metallic element, and B
indicates a tetravalent metallic element).
18. The sound output apparatus of claim 16 or 17, wherein the seed
composition is oriented with a length of 1 .mu.m to 50 .mu.m in at
least one direction.
19. The sound output apparatus of claim 1, further comprising a
weight member disposed on at least one area of the second sound
output unit.
20. The sound output apparatus of claim 1, wherein the first and
second sound output units are driven at the same voltage of
approximately 0.1V to approximately 5V.
21. The sound output apparatus of claim 1, wherein a space between
the first and second sound output units has a volume of 10 mm.sup.3
to 100 mm.sup.3.
22. The sound output apparatus of any one of claims 1 to 9, 12-17,
19, and 21, further comprising a coating layer disposed on at least
a portion of at least one of the first sound output unit, the
second sound output unit, and the housing.
Description
1. TECHNICAL FIELD
[0001] The present disclosure relates to a sound output apparatus,
and more particularly, to a sound output apparatus capable of
improving output characteristics of an audio frequency band
including a low-pitched sound band and a high-pitched sound
band.
2. DESCRIPTION OF RELATED ART
[0002] In general, a piezoelectric element represents an element
having characteristics mutually converting electrical energy and
mechanical energy to each other. That is, the piezoelectric element
generates a voltage when a pressure is applied (piezoelectric
effect) and generates an increase or decrease in volume or length
due to a pressure variation therein when a voltage is applied
(inverse piezoelectric effect). The piezoelectric element includes
a piezoelectric layer and an electrode disposed thereon and has a
pressure varied in accordance with a voltage applied to the
piezoelectric layer through the electrode.
[0003] The piezoelectric element may be used to manufacture various
components such as a piezoelectric speaker and a vibration device.
Among those, the piezoelectric speaker acoustically converts
mechanical movement of the piezoelectric element by a vibration
plate to generate a sound in a desired frequency band. The
piezoelectric speaker has an advantage in that it is thinner and
lighter than a conventional dynamic speaker and has a low power
consumption. Accordingly, the piezoelectric speaker may be used for
electronic devices such as a smartphone, which require a small
size, a thin-type, and a light weight. However, the piezoelectric
speaker has a disadvantage in that it has difficulties in listening
to music for a long time because it has a strong high-pitched sound
and a weak low-pitched sound.
[0004] Meanwhile, a dynamic speaker widely used for playing music
uses a principle in which when a voice signal current flows in a
voice coil in a magnetic field of a magnet, mechanical force acts
on the voice coil in accordance with an intensity of the current to
generate movement. However, the dynamic speaker is appropriate for
realizing a low-pitched sound but relatively weak for realizing a
high-pitched sound, and thus has a limitation to provide a high
quality sound.
[0005] Accordingly, the applicant of the present disclosure applied
for a patent for a sound output apparatus in which the
piezoelectric speaker and the dynamic speaker are coupled to each
other (Korean Patent Application No. 2015-0171719). In the sound
output apparatus that is applied for a patent by the applicant, the
piezoelectric speaker and the dynamic speaker are spaced apart from
each other in a housing, and a discharge hole is defined in a
predetermined area of the housing to discharge an output sound from
the dynamic speaker. Accordingly, sounds respectively outputted
from the piezoelectric speaker and the dynamic speaker are not
mixed inside the housing and are mixed outside the housing. That
is, the sound of the piezoelectric speaker is directly outputted,
the sound of the dynamic speaker is outputted through the discharge
hole, and then the two sounds are mixed outside the housing.
[0006] However, the sound output apparatus has a limitation in
reducing its size. That is, since the sound of the piezoelectric
speaker is directly outputted, but the discharge hole needs to be
defined to output the sound of the dynamic speaker, a total size,
i.e., a size of housing is limited to be reduced. Alternatively, as
the size of the housing is reduced, the sizes of the piezoelectric
speaker and the dynamic speaker may be reduced. However, in this
case, sound characteristics are degraded.
PRIOR DOCUMENTS
Patent Documents
[0007] Korean Patent Publication No. 2014-0083860
[0008] Korean Patent Registration No. 10-1212705
Technical Problem
[0009] The present disclosure provides a sound output apparatus
having all advantages of a piezoelectric speaker and a dynamic
speaker.
[0010] The present disclosure also provides a sound output
apparatus capable of reducing a total size thereof and improving
all of low-pitched sound characteristics and high-pitched sound
characteristics.
[0011] The present disclosure also provides a sound output
apparatus capable of maintaining a size of a piezoelectric speaker
and reducing a size of a housing to maintain sound characteristics
and reduce a total size
Technical Solution
[0012] In accordance with an exemplary embodiment, a sound output
apparatus includes: a first sound output unit; a second sound
output unit spaced a predetermined distance from the first sound
output unit; at least one opening defined in the second sound
output unit; and a housing for accommodating at least one of the
first and second sound output units, in which the housing has an
external diameter that is 100% to 130% of a diameter of the second
sound output unit.
[0013] The first sound output unit may include a dynamic speaker,
and the second sound output unit may include a piezoelectric
speaker including a piezoelectric element and a vibration
plate.
[0014] The housing may have an external diameter that is 100% to
130% of a diameter of the piezoelectric element.
[0015] The vibration plate may have a diameter equal to or less
than the external diameter of the housing.
[0016] The external diameter of the housing may be less than 13
mm.
[0017] The opening may have a diameter that is 3% to 70% of that of
the piezoelectric element.
[0018] The piezoelectric element may include a base, a plurality of
piezoelectric layers disposed on at least one surface of the base,
a plurality of internal electrodes disposed between the plurality
of piezoelectric layers, and an external electrode disposed on the
outside so as to be connected to the plurality of internal
electrodes.
[0019] The base may have a thickness that is one-third to one-one
hundred fiftieth of that of the piezoelectric element.
[0020] Each of the piezoelectric layers may have a thickness of 2
.mu.m to 50 .mu.m.
[0021] The piezoelectric layer may be laminated in two layers to
fifty layers.
[0022] Each of the piezoelectric layers may have a thickness that
is one-third to one-one hundredth of that of the piezoelectric
element.
[0023] Each of the piezoelectric layers may have a thickness equal
to or greater than that of each of the internal electrodes.
[0024] The piezoelectric layer may include at least one pore.
[0025] The internal electrode may have at least one area having a
different thickness.
[0026] The internal electrode may have a surface area that is 10%
to 97% of that of the piezoelectric layer.
[0027] The piezoelectric layer may include a seed composition.
[0028] The piezoelectric layer may include an oriented base
material composition made of a piezoelectric material having a
perovskite crystal structure and a seed composition made of an
oxide distributed in the oriented base material composition and
having a general formula of ABO.sub.3 (A indicates a divalent
metallic element, and B indicates a tetravalent metallic
element)
[0029] The seed composition is oriented with a length of 1 .mu.m to
50 .mu.m in at least one direction.
[0030] A space between the first and second sound output units may
have a volume of 10 mm.sup.3 to 100 mm.sup.3.
[0031] The sound output apparatus may further include a weight
member disposed on at least one area of the second sound output
unit.
[0032] The weight member may further include a mesh disposed on an
area corresponding to the opening.
[0033] The sound output apparatus may further include a coating
layer disposed on at least a portion of at least one of the first
sound output unit, the second sound output unit, and the
housing.
Advantageous Effects
[0034] The sound output apparatus in accordance with exemplary
embodiments includes the dynamic speaker and the piezoelectric
speaker, which are spaced a predetermined distance from each other
in the housing. Accordingly, as the dynamic speaker having
excellent low-pitched sound characteristics and the piezoelectric
speaker having high-pitched sound characteristics are disposed in
the single housing, the sound characteristics in the audio
frequency band may be improved.
[0035] Also, as at least one opening is defined in the
predetermined area of the piezoelectric speaker, the sound
outputted from the dynamic speaker is outputted through the
opening. Accordingly, the sounds respectively outputted from the
dynamic speaker and the piezoelectric speaker are mixed outside the
housing to further improve the sound quality.
[0036] In addition, as the opening is defined in the predetermined
area of the piezoelectric speaker, the opening may not be defined
in the housing, and thus, the housing may be reduced in size. Thus,
the piezoelectric speaker may maintain the size thereof to maintain
the sound characteristics and reduce the size of the housing, and
thus, the total size of the sound output apparatus may be
reduced.
[0037] Meanwhile, the sound output apparatus in accordance with the
exemplary embodiment may be realized as a speaker and an earphone
In particular, the sound output apparatus in accordance with the
exemplary embodiment may be realized as an earphone to perform the
miniaturization of the earphone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Exemplary embodiments can be understood in more detail from
the following description taken in conjunction with the
accompanying drawings, in which:
[0039] FIGS. 1 to 3 is an exploded perspective view, a coupling
perspective view, and a coupling cross-sectional view of a sound
output apparatus in accordance with an exemplary embodiment;
[0040] FIG. 4 is a perspective view illustrating a modified example
of the sound output apparatus in accordance with the exemplary
embodiment;
[0041] FIG. 5 is a perspective view in accordance with an exemplary
embodiment of a piezoelectric element used in an exemplary
embodiment;
[0042] FIGS. 6 through 9 are cross-sectional views in accordance
with an exemplary embodiment of the piezoelectric element used in
an exemplary embodiment;
[0043] FIGS. 10 and 11 are graphs showing sound characteristics in
accordance with a thickness and the number of lamination of a
piezoelectric layer of a piezoelectric element;
[0044] FIGS. 12 through 14 are views for explaining a
characteristics of a piezoelectric ceramic sintered body used in an
exemplary embodiment;
[0045] FIGS. 15 through 17 are views for explaining an exemplary
embodiment and a comparative example of the piezoelectric ceramic
sintered body used in an exemplary embodiment;
[0046] FIGS. 18 and 19 are an exploded perspective view and a
coupling perspective view of a sound output apparatus in accordance
with another exemplary embodiment;
[0047] FIGS. 20 and 21 are an exploded perspective view and a
coupling perspective view of a sound output apparatus in accordance
with still another exemplary embodiment;
[0048] FIG. 22 is a graph illustrating characteristics of a sound
output apparatus in which an opening is defined in a piezoelectric
speaker in accordance with exemplary embodiments and a sound output
apparatus in which a discharge hole is defined in a housing in
accordance with a comparative example;
[0049] FIG. 23 is a graph showing sound characteristics of a
piezoelectric speaker in accordance with a volume of an inner space
of a sound output apparatus.
[0050] FIGS. 24 through 26 are an exploded perspective view, a
coupling perspective view, and a coupling cross-sectional view of a
sound output apparatus in accordance with even another exemplary
embodiment;
[0051] FIG. 27 is a schematic plan view of the sound output
apparatus in accordance with even another exemplary embodiment;
and
[0052] FIG. 28 is a graph showing characteristics of the sound
output apparatus in accordance with even another exemplary
embodiment and the sound output apparatus in accordance with the
comparative example.
DETAILED DESCRIPTION OF EMBODIMENTS
[0053] Hereinafter, specific embodiments will be described in
detail with reference to the accompanying drawings. The present
disclosure may, however, be embodied in different forms and should
not be construed as limited to the embodiments set forth herein.
Rather, these embodiments are provided so that this disclosure will
be thorough and complete, and will fully convey the scope of the
present disclosure to those skilled in the art.
[0054] FIG. 1 is an exploded perspective view of a sound output
apparatus in accordance with an exemplary embodiment, FIG. 2 is a
perspective view illustrating a coupled state, and FIG. 3 is a
cross-sectional view of the coupled state. Also, FIG. 4 is a
perspective view of a modified example of a first sound output unit
of the sound output apparatus in accordance with the exemplary
embodiment
[0055] Referring to FIGS. 1 to 4, the sound output apparatus in
accordance with the exemplary embodiment may include a first sound
output unit 100, a second sound unit 200 disposed on the first
sound output unit 100, and a housing 300 accommodating at least one
of the first sound output unit 100 and the second sound output unit
200. That is, the first and second sound output units 100 and 200
may be spaced a predetermined distance from each other in the
housing 300. Here, the first sound output unit 100 may include a
dynamic speaker including a voice coil 140 and a vibration member
150 to vibrate in accordance with current variation of the voice
coil 140, and using this, allow the vibration member 150 to
vibrate, thereby outputting a sound. Also, the second sound output
unit 200 may include a piezoelectric speaker including a
piezoelectric element 210 and a vibration plate 220 to acoustically
convert mechanical movement by the vibration plate 220.
[0056] 1. First Sound Output Unit
[0057] The first sound output unit 100 may have an approximately
circular shape having a predetermined thickness. As illustrated in
FIG. 3, the first sound output unit 100 may include a yoke 110
having an accommodation space and a frame 115, a magnet 120
disposed in the accommodation space in the yoke 110, a plate 130
disposed on the magnet 120, a voice coil 140 disposed between the
yoke 110 and the magnet 120 in the frame 115, a vibration member
150 disposed above the plate 130, of which an edge is fixed to the
frame 115, and to which the voice coil 140 is fixed.
[0058] The yoke 110 has an approximately circular shape having a
predetermined height, and the fame 115 is disposed above the yoke
110 and has an approximately circular shape having a predetermined
height. Here, the frame 115 may have a height and a width greater
than those of the yoke 110. Alternatively, the height of the frame
115 may be equal to or less than that of the yoke 110. Here, the
frame 115 may have an upper edge contacting at least one area of
the housing 300 and be accommodated in the housing 300. Also, the
magnet 120 and the plate 130 may be accommodated in the yoke 110,
the voice coil 140 is accommodated in the frame 115, and the
vibration member 150 may be disposed on the frame 115 to cover the
frame 115. The yoke 110 and the frame 115 serve to induce a
magnetic field provided by the magnet 120 to the plate 130 so that
the magnetic field provided by the magnet 120 is maximally affected
to the voice coil 140.
[0059] The magnet 120 is fixed to a bottom surface of the yoke 110.
That is, the magnet 120 has a bottom surface contacting and fixed
to the inner bottom surface of the yoke 110. The magnet 120 may
have a shape corresponding to an inner shape of the yoke 110. For
example, the inside of the yoke 110 has an approximately
cylindrical shape, and the magnet 120 has an approximately circular
column shape. Here, the magnet 120 may have a height equal to or
less than that of the yoke 110. Also, the magnet 120 may have a
diameter equal to or less than that of the yoke 110. Accordingly,
the magnet 120 may be spaced a predetermined distance from an inner
wall of the yoke 110 in the yoke 110.
[0060] The plate 130 is disposed on a top surface of the magnet
120. The plate 130 may have the same shape as a planar shape of the
magnet 120. That is, the plate 130 may have a circular plate shape
having a predetermined thickness. Here, the plate 130 may have a
diameter less than that of the yoke 110 and equal to or greater
than that of the magnet 120. Accordingly, the plate 130 may have an
outer surface spaced a predetermined distance from an inner surface
of the yoke 110. Also, a height of the magnet 120 and the plate 130
disposed thereon may be equal to that of the yoke 110. That is, top
surfaces of the plate 130 and the yoke 110 may provide the same
plane. The plate 130 allows lines of magnetic force generated by
the magnet 120 to be focused toward the voice coil 140.
[0061] The voice coil 140 may be attached to a bottom surface of
the vibration member 150 and disposed between the yoke 110 and the
magnet 120 in the frame 115. For example, the voice coil 140 is
disposed between the plate 130/the magnet 120 and the yoke 110 to
surround a portion of the height of the plate 130 and the magnet
120 and has an upper portion attached to a bottom surface of the
vibration member 150. As the voice coil 140 provides a magnetic
field continuously varied by a continuously varying and inputted
electric signal, the voice coil 140 is vibrated by interaction
caused by an interference with the magnetic field provided by the
magnet 120.
[0062] The vibration member 150 has an edge fixed to the inner
surface of the frame 115 to cover an upper portion of the frame
115. Also, the vibration member 150 may have at least one
protruding area. For example, the vibration member 150 may have a
shape of which an area corresponding to a central area of the frame
115 is highest and gradually decreasing in height from the area to
the outside. That is, the vibration member 150 may have a
protruding shape gradually decreasing in height from an area
corresponding to a center of the magnet 120 and the plate 130 to
the outside. Also, the voice coil 140 may be fixed to a lowest area
of the vibration member 150
[0063] The first sound output unit 100 constitutes a closed circuit
in which a magnetic field generated from the magnet 120 is moved to
the yoke 110 therebelow through the plate 130 disposed on the
magnet 120 and then moved again to the magnet 120. The magnetic
field moved to a space between the plate 130 and the yoke 110
therebelow pulls or pushes the voice coil 140 in accordance with a
polarity of magnetic force of the voice coil 140 when current is
applied to the voice coil 140 and thus the voice coil 140 becomes
magnetic. That is, when the polarity of magnetic force of the voice
coil 140 is equal to that of the plate 130 and the yoke 110
therebelow, mutual repulsion occurs to push the voice coil 140, so
that the voice coil 140 moves forward. In addition, when the
polarity of magnetic force of the voice coil 140 is different from
that of the plate 130 and the yoke 110 therebelow, mutual
attraction occurs to pull the voice coil 140 backward. As described
above, when the voice coil 140 moves, the vibration member 150
fixed to the voice coil 140 moves back and force to vibrate the
air, thereby generating a sound.
[0064] 2. Second Sound Output Unit
[0065] The second sound output unit 200 may include a piezoelectric
element 210, a vibration plate 220, at least one opening 230
passing through a predetermined area of the second sound output
unit 200. That is, the opening 230 may be defined to pass through
the predetermined area of each of the piezoelectric element 210 and
the vibration plate 220. The piezoelectric element 210 may have,
e.g., a circular plate shape having a predetermined thickness.
Alternatively, the piezoelectric element 210 may have various
shapes such as a square shape, a rectangular shape, an oval shape,
and a polygonal shape in addition to the circular shape. The
piezoelectric element 210 may include a base and a piezoelectric
layer provided on at least one surface of the base. The
piezoelectric element 210 will be described in more detail with
reference to FIGS. 6 and 7 and the like. The piezoelectric element
210 is attached to at least one surface of the vibration plate 220
by using adhesive. Here, the piezoelectric element 210 may be
attached to a central portion of the vibration plate 220 to allow
both sides of the vibration plate 220 to be remained with the same
length as each other. Also, the piezoelectric element 210 may be
attached to a top surface or a bottom surface of the vibration
plate 220. Alternatively, the piezoelectric element 210 may be
attached to each of the top and bottom surfaces of the vibration
plate 220. That is, although the piezoelectric element 210 is
attached to the top surface of the vibration plate 220 in the
present embodiment, the piezoelectric element 210 may be attached
to the top surface of the vibration plate 220 or each of the top
and bottom surfaces of the vibration plate 220. Here, the
piezoelectric element 210 and the vibration plate 220 may be fixed
to each other through various methods in addition to adhesion. For
example, the vibration plate 220 and the piezoelectric element 210
are stuck to each other by using a stick agent, and side surfaces
of the vibration plate 220 and the piezoelectric element 210 are
attached to each other by using adhesive. Meanwhile, an electrode
pattern (not shown) to which a driving signal is applied may be
provided on an upper portion of one surface of the piezoelectric
element. At least two electrode patterns may be provided to be
spaced from each other and connected to a connecting terminal (not
shown) to receive an acoustic signal from an electronic device such
as an auxiliary mobile device through the connecting terminal.
[0066] The vibration plate 220 may have an approximately circular
plate shape and greater in size than the piezoelectric element 210.
Also, the vibration plate 220 may have an opening defined in a
central portion thereof, and the piezoelectric element 210 may be
provided on the opening. The piezoelectric element 210 may be
attached to a top surface of the vibration plate 220 using
adhesive. The vibration plate 220 may be manufactured by using
metal, plastic, and the like and by stacking different kinds of
materials to have a double structure. Also, the vibration plate 220
may be made of a polymer-based or pulp-based material. For example,
the vibration plate 220 may be made of a resin film. That is, the
vibration plate 200 may be made of a material having a large loss
coefficient with a Young's modulus of 1 MPa to 10 MPa such as an
ethylene propylene rubber-based material and a styrene butadiene
rubber-based material. Also, the vibration plate 220 may have a
lower edge contacting an inner surface of the housing 300. That is,
the vibration plate 220 and the piezoelectric element 210 attached
to a central portion thereof may be disposed in an inner space of
the housing 300. The second sound output unit 200 may be driven in
accordance with a predetermined signal and output sound having
excellent characteristics of high frequency sound Here, the
piezoelectric element 210 has a diameter equal to or less than that
of the vibration plate 220.
[0067] The opening 230 may be defined in at least one predetermined
area of the second sound output unit 200. That is, at least one
opening 230 may be defined to pass through the predetermined area
of each of the piezoelectric element 210 and the vibration plate
220. That is, the opening 230 may include a first opening 231
defined in at least one area of the piezoelectric element 210 and a
second opening 232 defined in at least one area of the vibration
plate 220. The opening 230 may be defined in accordance with a
shape of each of the piezoelectric element 210 and the vibration
plate 220. For example, the opening 230 may have a circular shape.
However, the opening 230 may have a shape different from that of
each of the piezoelectric element 210 and the vibration plate 220.
That is, the opening 230 may have various shapes such as a square
shape, a rectangular shape, an oval shape, and a polygonal shape.
Also, the first opening 231 and the second opening 232 may be
defined in, e.g., the central area of each of the piezoelectric
element 210 and the vibration plate 220 and overlap each other.
That is, the first opening 231 and the second opening 232 may have
the same size as each other and overlap each other. Alternatively,
the first and second openings 231 and 232 may be different in size,
and preferably, the central areas thereof may be overlapped with
each other. That is, although the vibration plate 220 may be
greater in size than the piezoelectric element 210, and the second
opening 232 defined in the vibration plate 220 may be greater than
the first opening 231 defined in the piezoelectric element 210, the
first opening 231 may be defined to overlap the second opening 232.
Accordingly, when the first and second openings 231 and 232
respectively defined in the piezoelectric element 210 and the
vibration plate 220 are different in size, the opening 230 has a
smaller size of that of each of the first and second openings 231
and 232. Alternatively, the opening 230 may be defined to a
different area except for the central area of each of the
piezoelectric element 210 and the vibration plate 220. Also, the
opening 230 may be defined in plurality. For example, as
illustrated in FIG. 4, a plurality of first openings 231a and 231b
may be defined in the central area and a surrounding area of the
piezoelectric element 210, and a plurality of second openings 232a
and 232b may be defined in the central area and a surrounding area
of the vibration plate 220. Here, at least one of the plurality of
openings 230 may be different in size. That is, at least one of the
plurality of first openings 231 defined in the piezoelectric
element 210 may be different in size, and at least one of the
plurality of second openings 232 defined in the vibration plate 220
may be different in size. For example, as illustrated in FIG. 4,
the first and second openings 231a and 232a defined in the central
area may be greater than at least one first and second opening 231b
and 232b, and at least one first and second opening 231b and 232b
defined in the surrounding area may have the same size as each
other or at least one thereof may be different in size. Here, each
of the plurality of first openings 231a and 231b and the plurality
of the second openings 232a and 232b may overlap each other.
Alternatively, the openings 230 respectively define din the
piezoelectric element 210 and the vibration plate 220 and
overlapping each other desirably have the same size as each other.
Each of the openings 230 may have a size of, e.g., 0.09% to 50% of
a surface area of the piezoelectric element 210. That is, at least
one opening 230 may have a size of 0.09% to 50% of the surface area
of the piezoelectric element 210. Here, when the opening 230 is
provided in plurality, a total surface area of the plurality of
openings 230 may have a size of 0.09% to 50% of the surface area of
the piezoelectric element 210. Alternatively, the opening 230 may
have a diameter that is 3% to 70% of that of each of the
piezoelectric element 210 and the vibration plate 220. That is,
when the piezoelectric element 210 has a circular shape, and the
opening 230 also has a circular shape, the opening 230 may have a
diameter that is 3% to 70% of that of the piezoelectric element
210. For example, when the piezoelectric element 210 has a diameter
of 10 mm, the opening 230 may have a diameter of 0.3 mm to 7 mm.
Alternatively, when the opening 230 has a polygonal shape, the
opening 230 may have an average diameter that is 3% to 70% of a
diameter B of the piezoelectric element 210. Meanwhile, the opening
230 defined in the vibration plate 220 may be defined in the same
position with the same size as the opening 230 defined in the
piezoelectric element 210. Alternatively, the opening 230 defined
in the vibration plate 220 may be defined greater or less in size
than the opening 230 defined in the piezoelectric element 220. When
the opening 230 has a size less than 0.09% or a diameter less than
3% of the surface area or the diameter of the piezoelectric element
210, sound characteristics may be reduced because an amount of the
sound outputted from the first sound output unit 100 and discharged
through the opening 230 is small. When the opening 230 has a size
greater than 50% or a diameter greater than 70%, piezoelectric
characteristics of the piezoelectric element 210 and vibration
characteristics of the vibration plate 220 may be hindered to
decrease the sound characteristics. As the opening 230 is defined
in the second sound output unit 200, the sound outputted from the
first sound output unit 100 may be outputted through the opening
230. Accordingly, the sound outputted from the second sound output
unit 200 and the sound outputted from the first sound output unit
100 and outputted through the opening 230 are mixed outside the
housing, so that the sound characteristics in an audio frequency
band may be further improved.
[0068] Meanwhile, a coating layer (not shown) may be further
provided on at least a portion of the second sound output unit 200.
The coating layer may be made of parylene and the like. The
parylene may be provided on a top surface and a side surface of the
piezoelectric element 210 and a top surface and a side surface of
the vibration plate 220 exposed by the piezoelectric element 210 in
a state in which the piezoelectric element 210 is attached on the
vibration plate 220. That is, the pyrylene may be provided on the
top and side surfaces of the piezoelectric element 210 and the
vibration element 220. Also, the parylene may be provided on the
top and the side surfaces of the piezoelectric element 210 and the
top, side, and bottom surfaces of the vibration plate 220 in a
state in which the piezoelectric element 210 is attached on the
vibration plate 220. That is, the parylene may be provided on the
top, side, and bottom surfaces of each of the piezoelectric element
210 and the vibration element 220. Also, when the piezoelectric
element 210 is provided on the opening defined in the central
portion of the vibration element 220, the parylene may be provided
on the top and side surfaces and the bottom surface, which is
exposed by the opening, of the piezoelectric element and, at the
same time, provided on the top, side, and bottom surfaces of the
vibration element 220. As the parylene is provided on at least one
surface of the piezoelectric element 210 and the vibration plate
220, moisture may be prevented from being introduced into the
second sound output unit 200, and thus oxidation may be prevented.
In addition, eccentric vibration generated by using a vibration
element made of a thin material such as a polymer may be improved,
and a response speed may be improved due to increase in hardness of
the vibration element to relieve deep acoustic characteristics and
stabilize upper register. Also, as a resonant frequency may be
adjusted in accordance with a coating thickness of the parylene, a
sound pressure improvement point is adjustable. Alternatively, the
parylene may be applied on only the piezoelectric element 210,
i.e., on the top, side, and bottom surfaces of the piezoelectric
element 210. In addition, the parylene may be applied on FPCB
coupled to the piezoelectric element 210 to supply power to the
piezoelectric element 210. As the parylene is provided on the
piezoelectric element 210, moisture may be prevented from being
introduced into the piezoelectric element, and thus oxidation may
be prevented. Also, as formation thickness is adjusted, the
resonant frequency may be adjusted. Meanwhile, when the parylene is
provided on the FPCB, noise generated from a joint between the
FPCB, a solder, and an element may be improved. The above-described
parylene may be applied with different thicknesses in accordance
with materials and features of the piezoelectric element or the
vibration element. For example, the parylene may have a thickness
less than that of the piezoelectric element or the vibration
element, e.g., a thickness of about 0.1 .mu.m to about 10 .mu.m.
For example, to apply the parylene, when the parylene is vaporized
by being first-heated in a vaporizer and converted into a dimmer
state, and then thermally decomposed into a monomer state by being
second-heated and cooled, the parylene may be converted from the
monomer state into the polymer state and applied at least one
surface of the piezoelectric vibration member 2. Meanwhile, the
waterproof layer such as the parylene may be applied to at least a
portion of the first sound output unit 100 and at least a portion
of the housing 200 as well as at least a portion of the second
sound unit 200.
[0069] 3. Housing
[0070] The housing 300 may have an approximately cylindrical shape.
That is, the housing 300 may have an approximately circular
container shape that is opened in at least one direction. For
example, the housing 300 may have a vertically through-type or a
shape having a closed inner predetermined area and upper and lower
portions thereof are opened. The vertically through-type housing
300 may include a first member 310 having an approximately ring
shape having a predetermined thickness and a second member 320
provided in upward and downward directions from a predetermined
area of the first member 310. That is, the second member 320 may be
provided to surround the ring shaped first member 310.
Alternatively, when the first member 310 has a circular plate
shape, the housing 300 having a predetermined space on upper and
lower portions from the first member 310 may be realized by the
second member 320 surrounding the first member 310. Meanwhile, the
second member 320 may have a cut area (not shown) vertically
defined in a predetermined area thereof. For example, the second
member 320 may surround the first member 310 and be spaced apart
from the predetermined area. In the cut area, a signal line for
providing a signal to the second sound output unit 200 may be
provided. Here, the cut area of the second member 320 may have a
width, i.e., a distance between ends of the second member 320,
which is 1% to 5% of a width of the second member 320. That is, in
the present invention, while the cut area is defined to provide a
signal supply line connected to the second sound output unit 200, a
discharge hole for discharging sound outputted from the first sound
output unit 100 is not defined. As a result, the second member 320
may seal the inner space of the housing 300. Alternatively, the
second member 320 may have a predetermined hole defined in a side
surface thereof instead of the cut area. That is, the hole may be
defined in the second member 320, and the signal line may be
connected thereto through the hole. Alternatively, the signal line
may be connected in various manners. For example, the signal line
may be connected between the second sound output unit 200 and the
second member 320.
[0071] Also, a protruding part 330 may be provided inside the
second member 320. That is, the protruding part 330 may protrude
inward from an inner wall of the second member 320. Also, the first
member 310 may be seated on the protruding part 330. The first
member 310 and the second member 320 may be separately manufactured
and then attached to each other so that the first member 310 is
seated on the protruding part 330 of the second member 320 or may
be integrated with each other. Alternatively, the protruding part
330 may not be provided, and the first member 310 and the second
member 320 may be attached to each other or integrated with each
other so that an outer side of the first member 310 contacts an
inner side of the second member 320. In the housing 300, the second
sound output unit 200, i.e., the vibration plate 220 of the
piezoelectric speaker, may contact the top surface of the second
member 320, and the first sound output unit 100, i.e., the dynamic
speaker, may contact the bottom side of the protruding part 330.
That is, the first sound output unit 100 and the second sound
output unit 200 may be spaced apart from each other with the first
member 310, the protruding part 330, and the second member 320
disposed above the first member 310. Alternatively, when the
protruding part 330 may not be provided inside the second member
320, and the first member 310 contacts the inner wall of the second
member 320, the vibration plate 220 may contact the top surface of
the second member 320, and the first sound output unit 100 may
contact the bottom surface of the first member 310. That is, the
first sound output unit 100 and the second sound output unit 200
may face each other and be spaced as many as thicknesses of the
first member 310 and the second member 320 thereabove. Accordingly,
since the vibration plate 220 is disposed on the second member 320,
the vibration plate 220 may have a diameter that is the same as an
external diameter A of the second member 320. That is, the
vibration plate 220 may have the diameter that is the same as the
external diameter A of the housing 300. Here, the piezoelectric
element 210 may have a diameter B that is less than the external
diameter A of the housing 300 and an internal diameter of the
housing 300. As the sound from the second sound output unit 200 is
directly discharged to the outside, and the sound from the first
sound output unit 100 is discharged through the opening 230 of the
second sound output unit 200, the two sounds are mixed outside the
housing 300.
[0072] Meanwhile, a predetermined space may be defined between the
first and second sound output units 100 and 200. That is, as
illustrated in FIG. 3, an inner space C may be defined between the
first and second sound output units 100 and 200, which face each
other, and the second member 320 of the housing 300 surrounding
side surfaces therebetween. The inner space C may have a volume of
10 mm.sup.3 to 100 mm.sup.3, desirably 20 mm.sup.3 to 80 mm.sup.3,
more desirably 30 mm.sup.3 to 70 mm.sup.3. Here, the volume of the
inner space C may be adjusted by adjusting a position of the first
member 310. Alternatively, when the protruding part 330 is further
provided in the housing 300, the volume of the inner space C may be
adjusted by adjusting positions of the first member 310 and the
protruding part 330. The second sound output unit 200 may have a
resonant frequency adjusted in accordance with the volume of the
inner space C. That is, as the volume of the inner space C
increases, the resonant frequency of the second sound output unit
200 may be shifted to a low frequency band. However, since, as the
volume of the inner space C increases, the size of the housing 300
increases, and accordingly, the size of the sound output apparatus
increase, the inner space C may have a volume of 10 mm.sup.3 to 100
mm.sup.3 while not increasing the size of the housing.
[0073] The above-described sound output apparatus may be
manufactured as a speaker, an amplifier, and an earphone for a
vehicle speaker or a speaker for family use. Desirably, the sound
output apparatus in accordance with an exemplary embodiment may be
manufactured as an earphone such as a kernel-type earphone, and in
this case, the housing 300 may have an approximate size that is
insertable into an ear. Here, the sound output apparatus may be
inserted into the ear from the second sound output unit 200.
Accordingly, the sound from the second sound output unit 200 is
outputted first, and then sound from the first sound output unit
100 is outputted through the opening 230, so that the two sounds
are mixed in an ear. Also, in accordance with an exemplary
embodiment, the first sound output unit 100 and the second sound
output unit 200 may be inserted into and spaced apart from each
other in the housing 300, or a portion of the housing 300 into
which the first sound output unit 100 is inserted and another
portion of the housing 300 into which the second sound output unit
200 is inserted are coupled to each other to manufacture the sound
output apparatus. For example, the sound output apparatus may be
manufactured in such a manner that a thickness of the first member
310 is divided in half, the first sound output unit 100 is inserted
inside the first housing, which provides a portion of the second
member 320 to surround a first thickness of a lower side of the
first member 310, the second sound output unit 200 is inserted
inside the second housing, which provides a portion of the second
member 320 to surround a second thickness of an upper side of the
first member 310, and then the first and second housing are coupled
to each other.
[0074] Meanwhile, the sound output apparatus in accordance with an
exemplary embodiment may be driven at a low voltage of 0.1 V to 5.0
V, desirably, 0.1 V to 2.0 V, more desirably, 0.1V to 0.5V.
Especially, when applied to an earphone, the apparatus may be
driven at a low voltage of 0.1 V to 0.2 V, desirably 0.1 V to 0.18
V. That is, the piezoelectric element 210 of the second sound
output unit 200 is formed by stacking a plurality of piezoelectric
layers with an inner electrode therebetween. Here, since the
piezoelectric layer has a thickness of 1 .mu.m to 30 .mu.m, the
second sound output unit 200 may be driven at the low voltage.
While a conventional piezoelectric speaker has a driving voltage
equal to or greater than 5V, the second sound output unit 200 in
accordance with an exemplary embodiment may be driven at the low
voltage of 0.1V to 0.5V without using an additional amplifier for a
piezoelectric speaker, and accordingly, coupled to a dynamic
speaker and driven at the low voltage. Also, in the sound output in
accordance with an exemplary embodiment, the first and second sound
output units 100 and 200 may be driven at the same time by applying
the same signal thereto. That is, as a signal provided from a
signal source is directly applied to the first sound output unit
100, passes through a high band filter, and is applied to the
second sound output unit 200, signals in low frequency and high
frequency bands may be respectively applied to the first and second
sound output units 100 and 200. However, in accordance with an
exemplary embodiment, the same signal may be simultaneously applied
to the first and second sound output units 100 and 200.
[0075] Next, the piezoelectric element 210 used as the second sound
output unit 200 of the present invention will be described below in
detail with reference to the drawings. FIG. 5 is a perspective view
of a piezoelectric element in accordance with an exemplary
embodiment, and FIGS. 6 to 9 are cross-sectional views taken along
lines A-A', B-B', C-C', and D-D' in FIG. 5. Also, FIGS. 10 and 11
are views for explaining a piezoelectric element in accordance with
another exemplary embodiment.
[0076] 2.1. One Example of Piezoelectric Element
[0077] As illustrated in FIG. 5, the piezoelectric element 210 may
have a plate shape having a predetermined thickness. For example,
the piezoelectric element 210 may have a thickness of, e.g., 0.1 mm
to 1 mm. However, the piezoelectric element 210 may have a
thickness less or greater than the above-described thickness range
in accordance with a size of the sound output apparatus and/or a
size of the second sound output unit. Alternatively, the
piezoelectric element 210 may have a circular shape having a
diameter of, e.g., 4 mm to 15 mm. Here, the piezoelectric element
210 has a diameter equal to or less than that of the vibration
plate 220. Alternatively, the piezoelectric element 210 may have
various shapes such as a rectangular shape and an oval shape and a
shape different from that of the vibration plate 220. For example,
the vibration plate 220 may have a rectangular shape and the
piezoelectric element 210 may have a circular shape, or the
vibration plate 220 may have a circular shape and the piezoelectric
element 210 may have a rectangular shape. When the piezoelectric
element 210 and the vibration plate 220 have different shapes, the
piezoelectric element 210 is desirably less in size than the
vibration plate 220 so that at least one area of the piezoelectric
element 210 is not deviated to the outside from the vibration plate
220. Meanwhile, the piezoelectric element 210 may have various
shapes and a surface area of 10 mm.sup.2 to 200 mm.sup.2. The
surface area may be a total surface area of the piezoelectric
element 210 including the opening 230. Also, the surface area of
the piezoelectric element 210 excluding the opening may be 4
mm.sup.2 to 100 mm.sup.2.
[0078] As illustrated in FIGS. 6 to 9, the piezoelectric element
210 may include a base 2110, at least one piezoelectric layer 2120
provided on at least one surface of the base 2110, and at least one
internal electrode 2130 provided on the piezoelectric layer 2120.
Also, the piezoelectric element 210 may further include cover
layers 2140 (2141 and 2142) provided on a surface of a laminate in
which a plurality of piezoelectric layers 2120 are laminated and
external electrodes 2500 (2510, 2520, 2530, and 2540) provided
outside the laminate so as to be selectively connected to the
internal electrodes 2130. The piezoelectric element 210 may be
provided in a bimorph-type in which the piezoelectric layer 2120 is
provided on both surfaces of the base 2110 or an unimorph-type in
which the piezoelectric layer 2120 is provided on one surface of
the base 2110. Also, the piezoelectric element 210 may be provided
in an unimorph-type by laminating a plurality of piezoelectric
layers 2120 on one surface of the base 2110 to increase
displacement and vibration force and be driven at a low voltage.
For example, as illustrated in FIGS. 6 to 9, the plurality of
piezoelectric layers 2120 (2121 to 2126) may be laminated on one
surface and the other surface of the base 2110, and a conductive
layer is provided between the piezoelectric layers 2120 to provide
a plurality of internal electrodes 2130 (2131 to 2138). Meanwhile,
at least one of the internal electrodes 2130 may be provided on the
surface of the base 2110. Here, the base 2110 may be made of an
insulating material. Also, the piezoelectric element 210 may
further include external electrodes 2140 (2141 and 2142) provided
outside the laminate so as to be connected to the internal
electrodes 2130.
[0079] The base 2110 may use a material having a characteristic
maintaining the structure in which the piezoelectric layers 2120
are laminated and generating vibration. For example, the base 2110
may be made of a material such as metal, plastic, and insulating
ceramic. Also, the base 2110 may be made of the same kind of
material as that of the piezoelectric layer 2120. That is, the base
2110 may be made of a material such as metal, plastic, and
insulating ceramic, which is different from that of the
piezoelectric layer 2120, or the same kind of material as that of
the piezoelectric layer 2120. Here, the piezoelectric layer 2120
used as the base 2110 may not be polarized or may be polarized.
When the piezoelectric layer 2120 used as the base 2110 is
polarized, the base 2110 may serve as the piezoelectric layer 2120.
Also, the base 2110 may have a circular shape in accordance with
the shape of the piezoelectric element 210 and include the opening
230 at a central portion thereof. The base 2110 may have a
thickness that is one-third to one-one hundred fiftieth of a total
thickness of the piezoelectric element 210. For example, the base
2110 may have a thickness of 2 .mu.m to 200 .mu.m. Here, the
thickness of the base 2110 may be less than that of all of
piezoelectric layers 2120, and equal to or greater than that of
each of the plurality of laminated piezoelectric layers 2120.
Alternatively, the thickness of the base 2110 may be less than that
of each of the piezoelectric layers 2120. However, as the thickness
of the base 2110 increases, the thickness of the piezoelectric
layers 2120 may decrease or the number of lamination of the
piezoelectric layers 2120 may be reduced to generate small amount
of piezoelectric phenomenon. Thus, the thickness of the base 2110
is desirably less than that of all of the piezoelectric layers
2120.
[0080] Each of the piezoelectric layers 2120 may have the same
shape and the same size as those of base 2110. That is, the
piezoelectric layer 2120 may have a circular shape and has the
opening 230 at a central portion thereof. Here, the opening 230 of
the piezoelectric layer 2120 and the opening 230 of the base 2110
may have the same size and shape as each other. Also, the
piezoelectric layer 2120 may be laminated in two layers to seventy
layers, desirably two layers to fifty layers, more desirably six
layers to thirty layers. Here, a sound pressure may be adjusted in
accordance with the number of lamination of the piezoelectric layer
2120. That is, as the number of lamination increases, the sound
pressure may increase. However, when the piezoelectric layer 2120
is laminated in more than seventy layers, since the piezoelectric
element 210 increases in thickness, and the sound pressure slightly
increases, the piezoelectric layer 2120 is desirably laminated in
two layers to fifty layers, more desirably six layers to thirty
layers. Meanwhile, the piezoelectric layer 2120 may be laminated on
one surface and the other surface of the base 2110 with the same
number. For example, the first to third piezoelectric layers 2121
to 2123 may be laminated on one surface of the base 2110, and the
fourth to sixth piezoelectric layers 2124 to 2126 may be laminated
on the other surface of the base 2110. Also, each of the
piezoelectric layers 2120 may have a thickness of one-third to
one-one hundredth of the thickness of the piezoelectric element
210. For example, each of the piezoelectric layers 2120 may have a
thickness of 1 .mu.m to 300 .mu.m, desirably 2 .mu.m to 30 .mu.m,
more desirably 2 .mu.m to 20 .mu.m. The sound output apparatus
including the piezoelectric element 210 may be driven by a voltage
provided from an electronic device such as a portable electronic
device, e.g., a smartphone. Here, since the voltage provided from
the electronic device is too low, i.e., about 0.2 V, the
piezoelectric layer 2120 needs to have an approximate thickness to
maximize the performance of the piezoelectric element 210. Thus,
the thickness of the piezoelectric layer 2120 may be desirably 2
.mu.m to 30 .mu.m, more desirably 2 .mu.m to 20 .mu.m. The
piezoelectric layers 2120 may be made of, e.g., a PZT(Pb, Zr, Ti),
NKN(Na, K, Nb), or BNT(Bi, Na, Ti)-based piezoelectric material.
However, the piezoelectric layers 2120 may not be limited to the
above-described materials and may use various piezoelectric
materials. That is, the piezoelectric layers 2120 may use various
kinds of piezoelectric materials that generate a voltage when
pressure is applied thereto and generate increase or decrease in
volume or length due to pressure variation when a voltage is
applied. Meanwhile, each of the piezoelectric layers 2120 may
include a pore (not shown) defined in at least one area thereof.
Here, the pore may have at least one size and shape. That is, the
pore may have an irregular shape and size and be irregularly
distributed. Also, the piezoelectric layer 2120 may be polarized in
at least one direction. For example, two adjacent piezoelectric
layers 2120 may be polarized in different directions. That is, the
plurality of piezoelectric layers 2120 polarized in different
directions may be alternately laminated. For example, the first,
third, and fifth piezoelectric layers 2121, 2123, and 2125 are
polarized in a downward direction, and the second, fourth, and
sixth piezoelectric layers 2122, 2124, and 2126 may be polarized in
an upward direction.
[0081] The internal electrode 2130 may be provided to apply an
external voltage to the piezoelectric layers 2120. That is, the
internal electrodes 2130 may apply a first power for polarization
of the piezoelectric layers 2120 and a second power for driving the
piezoelectric layers 2120 to the piezoelectric layers 2120. The
first power for polarization and the second power for driving may
be applied to the internal electrodes 2130 through the external
electrode 2150. These internal electrodes 2130 may be respectively
provided between the base 2110 and the plurality of piezoelectric
layers 2120. Also, each of the internal electrodes 2130 may have a
circular shape in accordance with the shapes of the base 2110 and
the piezoelectric layers 2120. Alternatively, the internal
electrode 2130 may have a polygonal shape such as a rectangular
shape. Here, the internal electrode 2130 may be disposed on an area
except for an area on which the opening 230 is defined and spaced a
predetermined distance from an edge of the piezoelectric layer
2120. Also, the internal electrode 2130 may be spaced a
predetermined distance from the opening 230. Accordingly, the
internal electrode 2130 may have a surface area less than that of
the piezoelectric layer 2120. Also, the internal electrode 2130 may
be selectively connected to the external electrode 2150 disposed
outside the laminate in which the piezoelectric layers 2200 are
laminated. That is, two internal electrodes 2130 may be connected
to one external electrode 2150. For example, as illustrated in
FIGS. 6 to 9, the first and third internal electrodes 2131 and 2133
may be connected to a first external electrode 2151, the second and
fourth internal electrodes 2132 and 2134 may be connected to a
second external electrode 2152, the fifth and seventh internal
electrodes 2135 and 2137 may be connected to a third external
electrode 21, and the sixth and eighth internal electrodes 2136 and
2138 may be connected to a fourth external electrode 2154. For
this, the internal electrodes 2130 may include a lead electrode led
in a direction of the external electrodes 2150. That is, each of
the internal electrodes 2120 may include a main electrode having an
approximately circular shape in accordance with that of the
piezoelectric layer 2200 and a lead electrode led in a direction of
the external electrodes 2150 with a predetermined width from a
predetermined area of the main electrode. In FIGS. 6 to 9, a
portion having the same size in a vertical direction of the
internal electrodes 2130 is the main electrode, and a portion
further extending to be connected to the external electrode 2150 is
the lead electrode. Meanwhile, each of the internal electrodes 2130
may be made of a conductive material including, e.g., metal
containing at least one of Al, Ag, Au, Pt, Pd, Ni, and Cu or a
metallic alloy thereof. In case of an alloy, for example, an alloy
of Ag and Pd may be used. Meanwhile, the internal electrode 2130
may have a thickness equal to or less than that of the
piezoelectric layer 2120, e.g., a thickness of 1 .mu.m to 10 .mu.m.
Here, at least one area of the internal electrode 2130 may have a
different thickness, or at least one area may be removed therefrom.
That is, the same internal electrodes 2130 may have at least one
area having a thickness greater or less than that of another area,
or at least one area may be removed from the internal electrode
2130 to expose the piezoelectric layer 2120. However, although at
least one area of the internal electrode 2130 has a greater or less
thickness or at least one area is removed therefrom, an overall
connection state may be maintained not to generate any problem in
electrical conductivity. Also, the different internal electrodes
2130 may have thicknesses different from each other in the same
area or have shapes different from each other That is, at least one
internal electrode 2130 in the same area corresponding to a
predetermined length and width in a vertical direction among the
plurality of internal electrodes 2130 may have a thickness or a
shape different from that of each of the internal electrodes 2130.
Here, the different shape may include a shape recessed, protruding,
or notched. Also, the each of the internal electrodes 2130 may have
a surface area of 10% to 97% of that of each of the piezoelectric
layers 2120. Meanwhile, the piezoelectric element 210 may have a
distance to the internal electrode 2130, which is one-tenth to
one-hundredth of a total thickness. That is, each of the
piezoelectric layers 210 between the internal electrodes 2130 may
be one-third to one-hundredth of a thickness of all of the
piezoelectric elements 210. For example, when each of the
piezoelectric elements 210 has a thickness of 300 .mu.m, a distance
between the internal electrodes 2130, i.e., a thickness of each of
the piezoelectric layers 2120 may be 3 .mu.m to 100 .mu.m. A
driving voltage may be varied by the distance between the internal
electrodes 2130, i.e., the thickness of the piezoelectric layer
2120, and the driving voltage may decrease as the distance between
the internal electrodes 2130 is closer. However, when the distance
between the internal electrodes 2130, i.e., the thickness of the
piezoelectric layer 2120, exceeds one-third of the total thickness
of the piezoelectric elements 210, the driving voltage may
increase, and accordingly, a high cost driving IC for generating a
higher driving voltage may be necessary to increase costs. Also,
when the distance between the internal electrodes 2130, i.e., the
thickness of the piezoelectric layer 2120, is less than
one-hundredth of the total thickness of the piezoelectric elements
210, thickness variation may frequently occur, and accordingly, the
thickness of the piezoelectric layer 2120 may not be constant to
decrease characteristics thereof.
[0082] The cover layer 2140 may be disposed on at least one of
bottom and top surfaces of the laminate. That is, the cover layer
2140 may include at least one of a lower cover layer 2141 disposed
on a lower portion of the laminate and an upper cover layer 2142
disposed on an upper portion of the laminate. The cover layer 2140
may be made of an insulating material, e.g., a piezoelectric
material that is not polarized. The internal electrodes 2130 may be
prevented from being oxidized by the cover layer 2140. That is, the
cover layer 2140 may be provided to cover the first and eighth
internal electrodes 2131 and 2138 that are exposed to the outside,
and oxygen or moisture may be prevented from being introduced by
the cover layers 2140 to prevent the oxidation of the internal
electrodes 2130.
[0083] The external electrodes 2150 may be provided to apply the
driving voltage for the piezoelectric layers 2120. For this, the
external electrodes 2150 may be provided on at least one surface of
the laminate and connected to the internal electrodes 2130. For
example, a plurality of external electrodes 2150 may be spaced a
predetermined distance from each other on a side surface of the
laminate. Alternatively, the external electrodes 2150 may extend on
at least one surface of the top and bottom surfaces as well as the
side surface of the laminate. The external electrodes 2150 may be
provided by using a method such as printing, deposition,
sputtering, and plating and provided as at least one layer. For
example, in each of the external electrodes 2150, a first layer
contacting the laminate may be formed by using a method of printing
using a conductive paste, and a second layer disposed thereabove
may be formed by a plating method. Also, at least one area of the
external electrodes 2150 connected to the internal electrodes 2130
may be made of the same material as that of the internal electrodes
2130. For example, the internal electrode 2130 may be made of
copper, and the first layer of the external electrode 2130
contacting the internal electrode 2140 and provided on the surface
of the laminate may be made of copper.
[0084] Characteristics of the piezoelectric speaker in accordance
with the thickness and the number of lamination of the
piezoelectric layer 2120 are illustrated in FIGS. 10 and 11. That
is, FIG. 10 is a graph showing sound characteristics in accordance
with the thickness of the piezoelectric layer, and FIG. 11 is a
graph showing sound characteristics in accordance with the number
of lamination of the piezoelectric layer.
[0085] To compare the sound characteristics in accordance with the
thickness of the piezoelectric layer, the sound characteristics are
measured when the thickness of the piezoelectric layer is 1 .mu.m,
2 .mu.m, 5 .mu.m, 10 .mu.m, 20 .mu.m, and 30 .mu.m with the same
number of lamination. As illustrated in FIG. 10, when the thickness
of the piezoelectric layer is 1 .mu.m, the sound characteristics
remarkably decreases at an about 6,000 Hz. Also, when the thickness
is 2 .mu.m to 30 .mu.m, the sound characteristics are excellent at
a frequency equal to or greater than 6,000 Hz. In particular, the
sound characteristics increases as the thickness decreases, and the
best sound characteristics are shown at the thickness of 2 .mu.m.
Also, when the thickness of the piezoelectric layer is 30 .mu.m,
the sound characteristics decreases in comparison with those when
the thickness is less than 30 .mu.m. Accordingly, the piezoelectric
layer have the excellent sound characteristics at the thickness
equal to or greater than 2 .mu.m and less than 30 .mu.m.
[0086] Also, to compare the sound characteristics in accordance
with the number of lamination of the piezoelectric layer, the sound
characteristics are measured when the piezoelectric layer is
laminated in 5 layers, 10 layers, 30 layers, and 50 layers with the
same thickness. As illustrated in FIG. 11, as the number of
lamination increases, the sound characteristics increase. That is,
when the number of lamination is equal to or greater than 30, the
sound characteristics increase in comparison with those when the
number of lamination is less than 30.
[0087] As a result, the sound characteristics increases as the
thickness of the piezoelectric layer 2120 decreases, and the number
of lamination of the piezoelectric layer 2120 increases.
[0088] 2.2. Another Example of the Piezoelectric Element
[0089] Meanwhile, the piezoelectric layer 2120 may use a
piezoelectric ceramic sintered body produced by sintering an
oriented base material composition made of a piezoelectric material
and a piezoelectric ceramic composition including a seed
composition made of an oxide distributed in the oriented base
material composition and having a general formula of ABO.sub.3 ((A
indicates a divalent metallic element, B indicates a tetravalent
metallic element). That is, the piezoelectric element 210 may
include a base 2110 and a piezoelectric layer 2120 and an internal
electrode 2130 disposed on at least one surface of the base 2110,
and the piezoelectric layer 2120 may include a piezoelectric
ceramic sintered body including a seed composition. Here, the
oriented base material composition may be made of a piezoelectric
material having a perovskite crystal structure. Also, the oriented
base material composition may use a composition in which a material
having a crystal structure different from the perovskite crystal
structure forms a solid solution. For example, a PZT-based material
in which PbTiO.sub.3[PT] having a tetragonal structure and
PbZrO.sub.3[PZ] having a rhombohedral structure form a solid
solution may be used.
[0090] Also, the oriented base material composition may use a
composition employing at least one of Pb(Ni,Nb)P.sub.3[PNN],
Pb(Zn,Nb)O.sub.3[PZN] and Pb(Mn,Nb)O.sub.3[PMN] as a relaxor in the
PZT-based material to improve characteristics of the PZT-based
material. For example, a PZNN-based material that uses a PZN-based
material and a PNN-based material in a PZT-based material to have
high piezoelectric characteristics, low dielectric constant, and
sinterability is employed as a relaxor to produce the oriented base
material composition. The oriented base material composition that
employs the PZNN-based material in the PZT-based material as the
relaxor may have a compositional formula of
(1-x)Pb(Zr.sub.0.47Ti.sub.0.53)O.sub.3-xPb((Ni.sub.1-yZn.sub.y).sub.1/-
3Nb.sub.2/3)O.sub.3. Here, x may have a value within a range of
0.1<x<0.5, desirably a value within a range of
0.30.ltoreq.x.ltoreq.0.32, most desirably a value of 0.31. Here, x
may have a value within a range of 0.1<x<0.5, desirably a
value within a range of 0.30.ltoreq.x.ltoreq.0.41, more desirably a
value of 0.40.
[0091] Since a piezoelectric ceramic sintered body shows remarkable
increase in piezoelectric characteristics in an area of a
morphotropic phase boundary (MPB), composition near the MPB is
necessary to be found. As composition of the oriented base material
composition that is sintered by adding a seed composition has a
phase different from that when the seed composition is not added,
and forms a new MPB composition in accordance with an amount of
addition of the seed composition, the excellent piezoelectric
characteristics may be induced. The MPB composition may be adjusted
by changing a value of x and a value of y. The MPB composition is
most desirable when x has a value of 0.31 and y has a value of 0.40
because the MPB composition has the highest piezoelectric
characteristics and dielectric characteristics.
[0092] Also, the oriented base material composition may use an
unleaded piezoelectric material that does not include lead (Pb).
The unleaded piezoelectric material may include at least one
piezoelectric material selected from the group consisting of
Bi.sub.0.5K.sub.0.5TiO.sub.3, Bi.sub.0.5Na.sub.0.5TiO.sub.3,
K.sub.0.5Na.sub.0.5NbO.sub.3, KNbO.sub.3, NaNbO.sub.3, BaTiO.sub.3,
(1-x)Bi.sub.0.5Na.sub.0.5TiO.sub.3-xSrTiO.sub.3,
(1-x)Bi.sub.0.5Na.sub.0.5TiO.sub.3-xBaTiO.sub.3,
(1-x)K.sub.0.5Na.sub.0.5NbO.sub.3-xBi.sub.0.5Na.sub.0.5TiO.sub.3,
and BaZr.sub.0.25Ti.sub.0.75O.sub.3.
[0093] The seed composition is formed of an oxide having a general
formula of ABO.sub.3. Here, ABO.sub.3 is an oxide having a
perovskite structure having orientation and a plate shape, where A
indicates a divalent metallic element and B indicates a tetravalent
metallic element. The seed composition produced by the oxide having
the general formula of ABO.sub.3 may include at least one of
CaTiO.sub.3, BaTiO.sub.3, SrTiO.sub.3, PbTiO.sub.3, and
Pb(Ti,Zr)O.sub.3 and be improved in piezoelectric performance when
BaTiO.sub.3 is used for the seed composition. When BaTiO.sub.3 is
used for the seed composition, BaTiO.sub.3 may be produced by
synthesizing Bi.sub.4Ti.sub.3O.sub.12 that is an aurivillius-type
templated structure in a molten salt synthesis method and
substituting through topochemical microcrystal conversion (TMC).
Here, the seed composition may be contained at a volume ratio of 1
vol % to 10 vol % with respect to the oriented base material
composition. When the seed composition is contained in the oriented
raw material composition with less than 1 vol %, an effect by which
crystal orientation is improved by the seed composition is
insignificant, and when greater than 10 vol %, the piezoelectric
performance of the piezoelectric ceramic sintered body decreases.
Here, when the seed composition is contained in the oriented base
material composition with 10 vol %, a strain amount may be
maximized to have optimized piezoelectric characteristics.
[0094] The piezoelectric ceramic composition including the oriented
base material composition and the seed composition is grown to have
the same orientation as that of the seed composition by templated
grain growth (TGG). That is, since as BaTiO.sub.3 is used as the
seed composition in the oriented base material composition having a
composition formula of
0.69Pb(Zr.sub.0.47Ti.sub.0.53)O.sub.3-0.31Pb((Ni.sub.0.6Zn.sub.0.4).sub.1-
/3Nb.sub.2/3)O.sub.3, sintering may be performed even at a low
temperature, the crystal orientation may be improved, and the
strain amount may be maximized, the piezoelectric ceramic sintered
body may have the high piezoelectric characteristics that is
similar to those of a single crystal material, That is, as the seed
composition improving the crystal orientation is added to the
oriented base material composition and then sintered to produce the
piezoelectric ceramic sintered body, the strain amount in
accordance with an electric field may be maximized, and the
piezoelectric characteristics may be remarkably improved.
[0095] Also, the piezoelectric ceramic sintered body in accordance
with another exemplary embodiment may have a Lotgering factor
having a value equal to or greater than 85%.
[0096] (a) of FIG. 12 is a graph showing a strain rate in
accordance with an electric field per Lotgering factor, and (b) of
FIG. 12 is a table showing an increase rate of the strain rate per
the Lotgering factor. Also, FIG. 11 is a graph showing a
piezoelectric constant d33 in accordance with the Lotgering
factor.
[0097] Referring to FIG. 12, the piezoelectric ceramic sintered
body increases in strain rate as the Lotgering factor increases.
That is, in case of the piezoelectric ceramic sintered body
(Normal), in which the crystal orientation is not performed, the
strain rate in accordance with the electric field has a value of
0.165%. When the crystal orientation increases by the templated
grain growth with respect to the piezoelectric ceramic sintered
body, the strain rate decreases to 0.106% by about 35.76% in the
piezoelectric ceramic sintered body, and as a value of the
Lotgering factor increases to 75%, 85%, and 90%, the strain rate
also increases to 0.170%, 0.190%, and 0.235%.
[0098] When the Lotgering factor of the piezoelectric ceramic
sintered body has the value equal to or greater than 85% with
respect to the maximum value 100%, the increase rate in accordance
with the electric field remarkably increases. That is, when the
Lotgering factor of the piezoelectric ceramic sintered body
increases from 75% to 85%, the increase rate has a value of about
12%. However, when the Lotgering factor of the piezoelectric
ceramic sintered body increases from 85% to 90%, the increase rate
has a value of about 27%, i.e., more than about four times.
[0099] Also, when the piezoelectric ceramic sintered body has a
value equal to or greater than 85%, the value of the piezoelectric
constant d33 remarkably increases. The piezoelectric constant d33
represents an amount of an electric charge generated in a pressure
direction when a pressure is applied to a material. As the
piezoelectric constant d33 has a higher value, high accuracy
piezoelectric element having an excellent sensitivity may be
produced. As illustrated in FIG. 13, when the Lotgering factor of
the piezoelectric ceramic sintered body increases from 75% to 85%,
the piezoelectric constant d33 increases from 345 pC/N to 380 pC/N
by 35 pC/N. However, when the Lotgering factor of the piezoelectric
ceramic sintered body increases from 85% to 90%, the piezoelectric
constant d33 increases from 380 pC/N to 430 pC/N by 50 pC/N, which
is more than three times increase rate. Accordingly, in case of the
piezoelectric ceramic sintered body in accordance with an exemplary
embodiment, as the piezoelectric ceramic sintered body is produced
by the oriented base material composition made of the piezoelectric
material having the perovskite crystal structure and the seed
composition made of the oxide distributed in the oriented base
material composition and having the general formula of ABO.sub.3 (A
indicates a divalent metallic element, B indicates a tetravalent
metallic element), the piezoelectric ceramic sintered body having
the Lotgering factor equal to or greater than 85% may be produced,
and the piezoelectric element having the improved strain rate and
the high sensitivity may be produced.
[0100] Characteristics (embodiment) of the piezoelectric layer with
the seed composition included in accordance with an exemplary
embodiment is compared with the piezoelectric layer without the
seed composition included. For the exemplary embodiment, powder of
PbO, ZrO.sub.2, TiO.sub.2, ZnO, NiO, Nb.sub.2O.sub.5, which have
more than 98% purity, is used to synthesize the oriented base
material composition of
0.69Pb(Zr.sub.0.47Ti.sub.0.53)O.sub.3-0.31Pb((Ni.sub.0.6Zn.sub.0.4).sub.1-
/3Nb.sub.2/3)O.sub.3. Also, Bi.sub.4Ti.sub.3O.sub.12 that is an
Orbilius templated structure is synthesized in a molten salt
synthesis method, and a BaTiO.sub.3 seed composition is synthesized
through a structural chemical microcrystal substitution. The seed
composition is mixed in the oriented base material composition with
10 vol % and then injected and molded to produce a piezoelectric
specimen. Also, the piezoelectric specimen increases in temperature
by 5.degree. C. per minute to perform a sintering process at a
temperature of 950.degree. C. for 10 hours. In comparison, the
comparative example is produced as same as the exemplary embodiment
except that BaTiO.sub.3 is not added as the seed composition. That
is, since BaTiO.sub.3 is not added in the comparative example, the
piezoelectric specimen without the seed composition is
produced.
[0101] FIG. 14 is a graph showing each of the piezoelectric ceramic
sintered bodies of the comparative example and the exemplary
embodiment, i.e., x-ray diffraction patterns of the piezoelectric
specimen .quadrature. of the comparative example and the
piezoelectric specimen .quadrature. of the exemplary embodiment. In
the graph, a degree of orientation is calculated in accordance with
a calculation formula of the Lotgering factor, and description
regarding the calculation formula for calculating the Lotgering
factor and the specific process will be omitted. As illustrated in
FIG. 14, the piezoelectric specimen .quadrature. of the comparative
example is grown in all crystal directions on a surface thereof,
and the crystal is remarkably grown in a normal direction of a
plane 110. Meanwhile, in the piezoelectric specimen .quadrature. of
the exemplary embodiment, crystal is grown in only a normal
direction of a plane 002 that is the same direction of a normal
direction of a plane 001 on a surface thereof, and the crystal
growth is restrained in the normal direction of the plane 110.
Also, a height of the graph represents an intensity of an x-ray
peak, and the Lotgering factor has a value of 95.3% in case of the
piezoelectric specimen .quadrature. of the exemplary embodiment.
Through this, in the piezoelectric ceramic sintered body including
the seed composition, the orientation is grown in the direction
001, and thus the crystal orientation is remarkably improved.
[0102] FIG. 15 is an image illustrating a scan electron microscope
image of the piezoelectric ceramic sintered body. That is, (a) of
FIG. 15 is a cross-sectional image of the piezoelectric specimen
produced by the comparative example, and (b) of FIG. 15 is a
cross-sectional image of the piezoelectric specimen produced by the
exemplary embodiment. As illustrated in (a) of FIG. 15, in case of
the piezoelectric ceramic sintered body without the seed
composition added, a grain is grown to have a hexagonal shape. This
result coincident with the result of FIG. 9, in which the crystal
is grown in each of plural planar directions. Meanwhile, as
illustrated in (b) of FIG. 15, the piezoelectric ceramic sintered
body with the seed composition added is grown to have a rectangular
shape by the seed composition (black area in (b) of FIG. 15) that
is horizontally disposed, so that the crystal orientation is
improved.
[0103] Also, FIG. 16 is a cross-sectional image of the
piezoelectric element using the piezoelectric ceramic sintered body
as the piezoelectric layer. That is, (a) of FIG. 16 is a
cross-sectional image of the piezoelectric specimen using the
piezoelectric ceramic sintered body as the piezoelectric layer in
accordance with the comparative example, and (b) of FIG. 16 is a
cross-sectional image of the piezoelectric specimen using the
piezoelectric ceramic sintered body as the piezoelectric layer in
accordance with the exemplary embodiment. As illustrated in (b) of
FIG. 16, the seed composition (black area in (b) of FIG. 16) exists
in the piezoelectric element using the exemplary embodiment, and as
illustrated in (a) of FIG. 16, the seed composition does not exist
in the piezoelectric element using the comparative example. Here,
the seed may be oriented to have a length of 1 .mu.m to 50 .mu.m in
one direction. That is, the orientation degree of the seed may be
oriented with about 1 .mu.m to 50 .mu.m respectively in one
direction and at least another direction, desirably 5 .mu.m to 20
.mu.m, more desirably 7 .mu.m to 10 .mu.m.
[0104] FIG. 17 is a graph showing sound characteristics of the
sound output unit including the piezoelectric element using the
piezoelectric ceramic sintered body as the piezoelectric layer. As
illustrated in FIG. 17, the exemplary embodiment with the seed
composition added is improved in sound characteristics in
comparison with the comparative example without the seed
composition added. That is, the sound pressure is improved by more
than 3 dB in a high-pitched band equal to or greater than 200
Hz.
[0105] Another Exemplary Embodiment of Sound Output Apparatus
[0106] FIG. 18 is an exploded perspective view of a sound output
apparatus in accordance with another exemplary embodiment, and FIG.
19 is a coupling perspective view of a sound output apparatus in
accordance with another exemplary embodiment Also, FIG. 20 is an
exploded perspective view of a sound output apparatus in accordance
with still another exemplary embodiment, and FIG. 21 is a coupling
cross-sectional view thereof.
[0107] Referring to FIGS. 18 through 21, the sound output apparatus
in accordance with another and still another exemplary embodiments
may include a first sound output part 100 including a voice coil
140 and a vibration member 150, a second sound part 200 disposed on
the first sound output part 100 and including a piezoelectric
element 210, a vibration plate 220, and an opening 230, and a
housing 300 accommodating at least one of the first and second
sound output units 100 and 200. Here, in accordance with another
and still another exemplary embodiments, the piezoelectric element
210 may be disposed below the vibration plate 220 to realize the
second sound output unit 200, i.e., a piezoelectric speaker. That
is, in accordance with an exemplary embodiment, the second sound
output unit 200 may be formed in such a manner that the
piezoelectric element 210 is disposed inside or outside the housing
300.
[0108] Also, as illustrated in FIGS. 20 and 21, the housing 300 may
include a first member 310 having a ring shape, a second member 320
surrounding the first member 310, and a protruding part 330
disposed below the first member 310. Here, the protruding part 330
may have a ring shape like the first member 310. Also, the
protruding part 330 may be less in size than an internal diameter
of the first member 310. Accordingly, the first member 310 may have
a diameter greater than that of the protruding part 330, and
accordingly, a stair-shaped stepped portion may be provided between
the first member 310, the protruding part 330, and the second
member 320. That is, the first member 310 may have the diameter
greater than that of the protruding part 330, and the second member
320 may have the diameter greater than that of the first member
310. Here, the second sound output unit 200 is seated on the first
member 310, and the first sound output unit 100 is coupled below
the protruding part 330. That is, the first sound output unit 100
and the second sound output unit 200 may be spaced apart from each
other with the first member 310 and the protruding part 330
therebetween. Alternatively, the second sound output unit 200 may
be seated on the protruding part 330. That is, the first and second
sound output units 100 and 200 may be spaced apart from each other
with the protruding part 330 therebetween.
[0109] As described above, the sound output apparatus in accordance
with exemplary embodiments may include the first sound output unit
100 and the second sound output unit 200 in the housing 300 to
improve low-pitched sound and high-pitched sound output
characteristics. That is, as the first sound output unit 100, i.e.,
the dynamic speaker, having excellent low-pitched characteristics
and the second sound output unit 200, i.e., the piezoelectric
speaker, having excellent high-pitched characteristics are disposed
in the housing 300, the sound characteristics in the audio
frequency band may be improved. Here, the sound output apparatus in
accordance with an exemplary embodiment may output a frequency of
20 Hz to 60 kHz. Also, as the opening 230 is defined in the second
sound output unit 200, the sound of the first sound output unit 100
may be outputted through the opening 230. Accordingly, the sound is
outputted from the second sound output unit 200, and then the sound
is outputted from the first sound output unit 100 through the
opening 230, so that the two sounds are mixed outside the housing
300. As the two sounds are mixed outside the housing 300, a sound
quality may be improved in comparison with a case in which sounds
are mixed in the housing 300.
[0110] Also, in the sound output apparatus in accordance with an
exemplary embodiment, since at least one opening 230 is defined in
the second sound output unit 200, the housing may be reduced in
size, and thus, the total size of the sound output apparatus may be
reduced. That is, according to Korean Patent Application No.
2015-0171719 applied for a patent by the present applicant, since a
discharge hole is necessarily defined in a predetermined area of a
housing to discharge an output sound of a dynamic speaker, the
housing is limited to be reduced in size. However, in accordance
with an exemplary embodiment, since a separate sound discharge hole
is not defined in the housing 300, and the sound of the first sound
output unit 100 is discharged through the opening 230 defined in
the second sound output unit 200, the housing may be reduced in
size. That is, while the piezoelectric element 210 of the second
sound output unit 200 is maintained, the external diameter of the
housing 300 may be reduced in size. As illustrated in FIG. 3, the
external diameter A of the housing 300 may be 20% of the diameter B
of the piezoelectric element 210. In other words, when the diameter
B of the piezoelectric element 210 is 100, the external diameter A
of the housing 300 may be equal to or greater than 100 and less
than 130, desirably, greater than 100 and equal to or less than
125, more desirably, equal to or greater than 105 and equal to or
less than 120. Here, when the diameter B of the piezoelectric
element 210 is equal to the external diameter A of the housing, the
piezoelectric element 210 and the vibration plate have the same
size, and a diameter of the vibration plate 220 is equal to the
external diameter of the housing 300. However, since an acoustic
conversion effect and an amplification effect of the vibration
plate 220 is reduced when the piezoelectric element 210 and the
vibration plate 220 have the same size as each other, the vibration
plate 220 is necessarily greater in size than the piezoelectric
element 210, and desirably, the vibration plate 220 is greater in
size by about 5% than the piezoelectric element 210. Accordingly,
since the diameter of the vibration plate 220 is equal to the
external diameter of the housing 300, when the diameter of the
piezoelectric element 210 is 100, the external diameter of the
housing 300 is desirably equal to or greater than 105. Also, when
the external diameter of the housing 300 is greater by 30% than the
diameter of the piezoelectric element 210, an effect in size
reduction of the sound output apparatus is reduced, so that the
external diameter of the housing 300 is desirably equal to or less
than 20% of the diameter of the piezoelectric element 210.
Resultantly, when the diameter of the piezoelectric element 210 is
100, the external diameter of the housing 300 is desirably 105 to
120. For example, when the diameter B of the piezoelectric element
210 is 10 mm, the external diameter A of the housing 300 may be
10.5 mm to 12 mm. Here, since the diameter of the vibration plate
220 may have the same size as the external diameter of the housing
300, when the diameter of the piezoelectric element 210 is 10 mm,
the external diameter A of the housing and the diameter of the
vibration plate 220 may be 10.5 mm to 12 mm. However, in Korean
Patent Application No. 2015-0171719 applied for a patent by the
present applicant, the diameter of the piezoelectric element 210 is
greater by 30% than the external diameter of the housing 300. For
example, when the diameter of the piezoelectric element 210 is 10
mm, the external diameter of the housing 300 according to Korean
Patent Application No. 2015-0171719 may be about 13 mm. This is
because the sound of the first sound output unit 100 is outputted
through the discharge hole defined in the housing 300. Accordingly,
in accordance with an exemplary embodiment, while the diameter of
the piezoelectric element 210 is maintained as it is, the external
diameter of the housing 300 may be reduced in comparison with other
inventions. For example, the external diameter of the housing may
be reduced by 10% to 20%. That is, when the external diameter of
the housing 300 in accordance with other inventions is 100, the
external diameter of the housing 300 in accordance with an
exemplary embodiment may be 80 to 90. Resultantly, in accordance
with an exemplary embodiment, the diameter of the piezoelectric
element 210 may be maintained as it is, the external diameter of
the housing 300 may be reduced, and thus the size of the sound
output apparatus may be reduced. Meanwhile, when the size of the
piezoelectric element 210 is reduced, the size of the housing 300
may be further reduced. That is, it is described that the size of
the housing 300 is 10.5 mm to 13 mm when the size of the
piezoelectric element 210 is 10 mm in the above-described exemplary
embodiment. However, the size of the piezoelectric element 210 may
be equal to or less than 10 mm, and accordingly, the size of the
housing 300 may be less than 13 mm. Accordingly, in accordance with
an exemplary embodiment, the size of the housing 300 may be less
than 13 mm, e.g., equal to or greater than 8 mm and less than 13 mm
regardless of the size of the piezoelectric element 210.
[0111] Table. 1 shows an opening in various sizes, an area ratio
according thereto, and sound characteristics of the sound output
apparatus using the same. Here, experiments are performed under a
condition in which the piezoelectric element 210 has a circular
shape having a diameter of 10 mm, and the opening has a size of 0.1
mm to 9 mm. Also, the opening having a circular shape is defined in
a central area of the piezoelectric element, and the opening is
also defined in the vibration plate at the same position with the
same size as that of the piezoelectric element 210. Meanwhile, in
the table. 1, "X" is marked when the sound characteristics are
degraded, "O" is marked when similar to that of the related art,
and ".circleincircle." is marked when improved in comparison with
that of the related art. As described in the table. 1, when the
diameter of the opening is 0.3 mm to 7 mm with respect to the
piezoelectric element having a diameter of 10 mm, i.e., a size
ratio is 3% to 70% or an area ratio is 0.09% to 50%, the sound
characteristics are similar or improved in comparison with those of
the conventional sound output apparatus. In particular, when a size
ratio of the opening to the piezoelectric element 10% to 20%, or an
area ratio thereof is 1% to 4%, the sound characteristics are
improved in comparison with those of the related art. The sound
characteristics further improved than those of the related art is
compared with the sound characteristics of the related art and
illustrated in FIG. 22.
TABLE-US-00001 TABLE 1 Size of opening (mm) Ratio of size (%) Ratio
of area (%) Result 0.1 1 0.01 X 0.3 3 0.09 0 0.5 5 0.25 0 1 10 1
.circleincircle. 1.5 15 2.25 .circleincircle. 2 20 4
.circleincircle. 3 30 9 .circleincircle. 4 40 16 0 5 50 25 0 6 60
36 0 7 70 49 0 8 80 64 X 9 90 81 X
[0112] FIG. 22 is a graph illustrating characteristics of a sound
output apparatus in which an opening is defined in a piezoelectric
speaker in accordance with exemplary embodiments and a sound output
apparatus in which a discharge hole is defined in a housing in
accordance with a comparative example. Here, the housing having an
external diameter of 13 mm and the piezoelectric element having a
diameter of 10 mm, and the dynamic speaker are applied together in
the comparative example, and the housing having an external
diameter of 11.2 mm and the piezoelectric element having a diameter
of 10 mm, and the dynamic speaker are applied together in an
exemplary embodiment. Also, the sound output hole having a size of
10 mm is defined in the housing in the comparative example, and the
opening having one of diameters of 1 mm, 1.5 mm, and 2 mm is
defined in the central portion of the second sound output unit in
the exemplary embodiment. In FIG. 22, the reference numeral 10 is a
characteristic graph in accordance with the comparative example,
and the reference numerals 20, 30, and 40 are characteristic graphs
when the opening having one of diameters of 1 mm, 1.5 mm, and 2 mm
is defined in the central portion of the second sound output unit
in accordance with the exemplary embodiment. As illustrated in FIG.
22, the sound output apparatuses 20, 30, and 40 in accordance with
an exemplary embodiment, in which the piezoelectric speaker, i.e.,
the piezoelectric element and the vibration plate, is defined, have
the higher sound characteristics in a frequency equal to or greater
than 2000 Hz than those of the sound output apparatus 10 in
accordance with the comparative example in which the opening is not
defined in the piezoelectric speaker and the discharge hole is
defined in the housing. Also, in a frequency equal to or greater
than 2500 Hz, as the diameter of the opening increases, the sound
characteristics increase. That is, in a frequency equal to or
greater than 2500 Hz, the sound characteristics in case that the
opening having the diameter of 2 mm is defined are greater than
those in case that each of the openings having the diameters of 1.5
mm and 1 mm is defined, and the sound characteristics are higher in
case that the opening having the diameter of 1.5 mm is defined than
those in case that the opening having the diameter of 1 mm is
defined. Accordingly, it is noted that the sound output apparatus,
in which the opening is defined in the piezoelectric speaker, in
accordance with an exemplary embodiment have the further improved
sound characteristics than the sound output apparatus in which the
discharge hole is defined in the housing. Also, the sound
characteristics in a specific frequency range may be improved in
accordance with the size of the opening. That is, the sound
characteristics may be adjusted improved in accordance with the
size of the opening.
[0113] Also, FIG. 23 is a graph showing characteristics of the
piezoelectric speaker in accordance with a volume of a space
between the dynamic speaker and the piezoelectric speaker. That is,
as illustrated in FIG. 3, the sound characteristics of the second
sound output unit 200 in accordance with the volume of the inner
space C defined between the first and second sound output units 100
and 200 by the housing 300 are compared and illustrated in FIG. 23.
As illustrated in FIG. 23, the sound characteristics are measured
when the volume of the inner space is 30 mm.sup.3 and 70 mm.sup.3,
and as the volume of the inner space increases, the resonant
frequency of the second sound output unit 200, i.e., the
piezoelectric speaker, may be shifted to a low frequency band. For
example, when the volume of the inner space is 30 mm.sup.3, the
resonant frequency is 8,000 Hz, and when the volume of the inner
space is 70 mm.sup.3, the resonant frequency is 6,000 Hz.
Accordingly, as the volume of the space between the dynamic speaker
and the piezoelectric speaker increases, the resonant frequency of
the piezoelectric speaker may be shifted to the low frequency
band.
[0114] Meanwhile, the sound output apparatus in accordance with an
exemplary embodiment may further include a weight member 240
disposed on at least one area of the second sound output unit 200.
For example, as illustrated in FIGS. 24 to 26, the sound output
apparatus in accordance with even another exemplary embodiment may
further include the weight member 240 disposed on at least one
surface of the vibration plate 220. That is, the piezoelectric
element 210 may be disposed on one surface of the vibration plate
220, and the weight member 240 may be provided on the other surface
thereof. Alternatively, the weight member 240 may be disposed on
the piezoelectric element 210. That is, the piezoelectric element
210 may be disposed on one surface of the vibration plate 220, and
the weight member 240 may be provided on the other surface thereof.
Here, the weight member 240 may be fixed on the vibration plate 220
or the piezoelectric element 210 by using a predetermined adhesion
member. The adhesion member may include a tape or an adhesive such
as a double sided tape, a cushion tape, an epoxy adhesive, a
silicone adhesive, and a silicone pad. Also, the weight member 240
may not block the opening 230. That is, an opening 233 may be
defined in the weight member 240 to correspond to openings 231 and
232 respectively defined in the piezoelectric element 210 and the
vibration plate 220 Here, the opening 233 define din the weight
member 240 may have the same size and shape as those of each of the
openings 231 and 232 respectively defined in the piezoelectric
element 210 and the vibration plate 220 or greater in size than the
piezoelectric element 210 and the vibration plate 220. That is, the
opening 233 equal to or greater than each of the openings 231 and
232 may be defined in the weight member 240 so that at least a
portion of the opening 230 is not blocked by the weight member 240.
Alternatively, the weight member 240 may be disposed on an area
spaced apart from the opening 230.
[0115] The weight member 240 may be made of a material having a
predetermined mass such as a metallic material. For example, the
weight member 240 may be made of a metallic material such as SUS
and tungsten that have a mass equal to or grater than that of the
piezoelectric element 210. As the weight member 240 having a
predetermined mass is provided on at least a portion of the second
sound output unit 200, a weight is loaded on the second sound
output unit 200. Accordingly, the vibration body, i.e., the
piezoelectric element 210 and/or the vibration element 220,
increases in weight as a result, and thus, the sound
characteristics may be further improved in comparison with those
when the weight member 240 is not used. That is, FIG. 28 is a graph
showing comparison between the sound characteristics of a
comparative example 50, in which the piezoelectric element 210 and
the vibration plate, which have the same size as each other, are
used, and the weight member 240 is not provided, and an exemplary
embodiment 60, in which the weight member 240 is provided. The
sound characteristics may be improved in the same frequency in the
exemplary embodiment 60 in comparison with the comparative example
50. Accordingly, when the weight member 240 is provided, the
piezoelectric element 210 may be reduced in size and the same sound
characteristics as those when the size of the piezoelectric element
210 is not reduced may be realized. That is, as the weight member
240 is provided, the piezoelectric element 210 having a second
diameter less than a first diameter may have the sound
characteristics that is the same as or similar to those of the
piezoelectric element 210 having the first diameter. As a result,
when the weight member 240 is provided, the resonant frequency may
decrease, and accordingly, the size of the second sound output unit
200, in particular, the size of the piezoelectric element 210, may
be reduced to reduce the total size of the sound output apparatus
in accordance with the exemplary embodiment. That is, the diameter
of the piezoelectric element 210 may be reduced, and accordingly,
the external diameter of the housing 300 may be reduced. Here, the
resonant frequency may be adjusted in accordance with the size and
mass of the weight member 240, and accordingly, the diameter of the
sound output apparatus, i.e., the external diameter of the housing
300 may be reduced by about 8 mm, more desirably, about 6 mm. That
is, the sound output apparatus in accordance with the exemplary
embodiment may have the external diameter of about 6 mm to about 13
mm.
[0116] Meanwhile, as illustrated in FIG. 27, a mesh structure may
be provided on the opening 233 of the weight member 240. That is,
the mesh structure may be made of the same material as that of a
portion contacting the vibration plate 220 and provided on the
opening 233. Here, the characteristics of the first sound output
unit 100 may be adjusted in accordance with a size of a pore of the
mesh. Here, the frequency characteristics of about 20 Hz to about 1
kHz may be adjusted in accordance with a size of a pore 241 of the
mesh. For example, the sound pressure may increase in the frequency
band when the size of the pore 241 is small, and the sound pressure
may decrease in the frequency band when the size of the pore 241 is
big.
[0117] As described above, as the weight member 240 is provided on
at least one area of the second sound output unit 200, the resonant
frequency of the piezoelectric element 210 may decrease.
Accordingly, the size of the piezoelectric element 210 may be
reduced at the same resonant frequency, and thus, the total size of
the sound output apparatus may be reduced.
[0118] As described above, the technical idea of the present
disclosure has been specifically described with respect to the
above embodiments, but it should be noted that the foregoing
embodiments are provided only for illustration while not limiting
the present disclosure. Various embodiments may be provided to
allow those skilled in the art to understand the scope of the
preset invention, but the present disclosure is not limited
thereto.
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